The formation of integral handles via the stretch-blow moulding process is highly desirable and the art contains a number of attempts to solve the inherent problems which have not proved successful. An integrally moulded handle is generally less expensive than a separate, e.g. clip-on, handle. Previously disclosed approaches to provide an integral handle typically require the formation of a pair of opposing depressions or cavities in the body of the bottle that form the structural basis of the handle. These depressions can either then be welded together and the central section, encompassed by the weld, can be removed such as to form a completely open space through which the fingers and/or thumb can be inserted (a ‘through’ handle), or, alternatively, left to simply form a grip. If the grip is formed to be sufficiently wide and deep so that a hand can close on the grip without having the tip of the fingers touch the bottom of the recess, then ergonomic studies have shown the resulting grip functionality to be as good as that of a through handle.
One approach to achieving this is disclosed in EP0346518B1, which is a process comprising a first step of blow moulding a preform in a mould cavity; then a second step of pressing and holding an area of the stretched preform between a pair of opposed movable projecting members within the blow mould, after the preform has expanded to substantially fill the inner cavity of the blow mould and before the preform has cooled to a temperature below the glass transition point of the resin.
A first problem with such a process is that the stretch-blow moulding and handle drawing steps must be performed in quick succession, otherwise the temperature decreases below the glass transition temperature. Maintenance of the temperature consumes a lot of energy and so is expensive.
It is an object of the present invention to provide a process to create a deep, concave grip which provides an ergonomic handle.
There is a need in the art for a process which is less energy intensive and in which the steps of stretch-blow moulding and handle drawing can be de-coupled. It is desirable to have a broader operating temperature range, rather than the necessity to maintain specific high temperatures. Therefore, the second step can be performed at a location away from the first step. There is also a need for the material to withstand high stresses during handle drawing to prevent material failure.